I'm building a fertilizing system and have 3 micropumps, 3-6V and 250-500mA
In another forum they suggested me to use a ULN2068 (here data)
I'm not skilled in using transistors so i've a couple of questions:
1_Do i need resistances for the four BASE ULN's pins?
2_Do i need any diodes for the motor's backforward current or the IC's buil-it ones are enough?
3_Do i need any capacitor for avoid motor's noisy? (100uF?)
Please, if yes, tell me where i have to solder theese components.
Thank you.
1_Do i need resistances for the four BASE ULN's pins?
2_Do i need any inductances for the motor's backforward current or the IC's buil-it ones are enough?
3_Do i need any capacitor for avoid motor's noisy? (100uF?)
No, the ULN has base resistors built in (see the 'Partial Schematic' at the bottom of the first page of the datasheet: Rin 2.5k).
Inductances, no. Diodes, yes.
The built-in diodes in the ULN can be used to protect the device. If you are running the motors from 6v, then that 6v should be connected to the ULN's Vs (14) and both K pins (1, 9). However, since you may have long wires to the motors themselves, it would be reasonable to fit additional diodes directly across each motor and...
Fitting a small capacitor (say, 0.1uF) directly across the motors (along with the diodes) will help reduce the amount of radiated 'noise'.
Yours,
TonyWilk
Yes, i meant diodes, not inductances (post corrected)
1_Nice.
2_I think i'll run the motor at 3V @250mA. Wires are really tiny (0.8mm diameter) and short as 10cm. Okay, i'll wire the battery.. :
-directly to Arduino RAW /Vcc
-directly to the motor
-to ULN's Vs and K pins
I'm Right?
Do you think i can avoid external diodes?
3_
TonyWilk:
No, the ULN has base resistors built in (see the 'Partial Schematic' at the bottom of the first page of the datasheet: Rin 2.5k).
Inductances, no. Diodes, yes.
The built-in diodes in the ULN can be used to protect the device. If you are running the motors from 6v, then that 6v should be connected to the ULN's Vs (14) and both K pins (1, 9). However, since you may have long wires to the motors themselves, it would be reasonable to fit additional diodes directly across each motor and...Fitting a small capacitor (say, 0.1uF) directly across the motors (along with the diodes) will help reduce the amount of radiated 'noise'.
Yours,
TonyWilk
squizzy91:
2_I think i'll run the motor at 3V @250mA. Wires are really tiny (0.8mm diameter) and short as 10cm. Okay, i'll wire the battery.. :
-directly to Arduino RAW /Vcc
-directly to the motor
-to ULN's Vs and K pins
I think there's a few of things to consider:
a. What Arduino are you using? What minimum voltage will it run at?
b. With 3 motors you'll have 0.75A at 3v so, unless it's a fairly large battery and you make the connections with thicker wire then you will end up with less than 3V.
c. The ULN is not a perfect switch, you could lose somewhere around 0.5v to 1.0v across the transistor, so your motor would only see, say, 2.5v.
Other than that, your description of the wiring sounds ok.
Yours,
TonyWilk
P.S. I don't think the external diodes and capacitors across the motors will be absolutely essential in this case.
A)
I'll use an Arduino Pro mini 3V
I wanna use 2x1,5V AAA, directly to Vcc (yes, i know i'm under specs) or maybe with an external 3v3 step up. Here we've to consider battery can reach 2-2.4V when discharged.
B)
Sorry i've not specified motors will run once a time. So 250mA of drain.
Transistor tension drainage is not a big problem but for calibration reason i need to take it in account. Is this drainage dependent from some parameter? Is this drainage written somewhere into the datasheet?
Thank you.
TonyWilk:
I think there's a few of things to consider:
a. What Arduino are you using? What minimum voltage will it run at?
b. With 3 motors you'll have 0.75A at 3v so, unless it's a fairly large battery and you make the connections with thicker wire then you will end up with less than 3V.
c. The ULN is not a perfect switch, you could lose somewhere around 0.5v to 1.0v across the transistor, so your motor would only see, say, 2.5v.Other than that, your description of the wiring sounds ok.
Yours,
TonyWilkP.S. I don't think the external diodes and capacitors across the motors will be absolutely essential in this case.
IMPORTANT: are theese connections right?
K, Vs ->+3V
GND->GND
B->ARDUINO PWM
C-> MOTOR->+3v
Note:
-For complexity reason in this photo there is only one motor
-i will use the same battery for feed the motors (one each a time), the IC and the Pro mini
Your connections look ok.
In the ULN datasheet, the parameter to look at is Vce(sat), that's the voltage which can be across the transistor when it is turned ON and sinking a given amount of current.
It's like the 'ON resistance' of the transistor.
The datasheet gives a Vce(sat) figure of 1.13V max for Ic = 500mA, so I estimated Vce(sat) of 0.5v - 1.0v at your current of 250mA.
Yours,
TonyWilk
There are MOSFET equivalents to the ULNs but I can't find them quickly.
If i've understood properly, what you mean is that 3V on K pins is too much.
1_what if i supply them not with the battery but with a pwm?
2_what if i supply them with the battery but insert a resistance?
3_if both are good, wich is the best solution?
*i will run motors at 500mA.
TonyWilk:
Your connections look ok.In the ULN datasheet, the parameter to look at is Vce(sat), that's the voltage which can be across the transistor when it is turned ON and sinking a given amount of current.
It's like the 'ON resistance' of the transistor.The datasheet gives a Vce(sat) figure of 1.13V max for Ic = 500mA, so I estimated Vce(sat) of 0.5v - 1.0v at your current of 250mA.
Yours,
TonyWilk
outsider:
There are MOSFET equivalents to the ULNs but I can't find them quickly.
LL-N-MOSFET?
squizzy91:
If i've understood properly, what you mean is that 3V on K pins is too much.
No... the 'Saturation Voltage' Vce(sat) is the voltage which is "lost" across the transistor, it depends on the current through the transistor - not the supply voltage. Your 3v supply is Ok.
This diagram might help explain it:
Yours,
TonyWilk
Here's what I was thinking about, don't know if it's appropriate for your project. 
Thank you all.
It was hard to understand what at least resulted simply once one have learnt the basics of transistor.
My issued where only if my project specs were suitable for that kind of IC's family and don't care about the voltage transistor drop (Vcesat).
I tested all and had theese results:
3.7Vin (lipo battery) -> 2.7V on micropump, sucking 150mA (1V drop).
Quite similar results with 3V AA battery.
